Added (visual) explanation for the different SmartShape textures

[stephanbogner]

As mentioned in Discord I think some kind of chart would help understanding what the different textures do.

• I wasn’t sure if people read anything outside the quickstart, so I put it there
• In my research I found out about Rayman Legends (and the UbiArt Framework). I thought it might be good to mention it so Google could pick it up, when people search for creating levels in that style in Godot.

Let me know what you think (and feel free to change the text).

Here is the Figma file in case (in the future) somebody needs to adjust the graphic itself:
SmartShape2D Docs.fig.zip

[mphe]

Thanks!